188 research outputs found
Crystallographic disorder and electron scattering on structural two-level systems in ZrAs1.4Se0.5
Single crystals of ZrAs1.4Se0.5 (PbFCl type structure) were grown by chemical
vapour transport. While their thermodynamic and transport properties are
typical for ordinary metals, the electrical resistivity exhibits a shallow
minimum at low temperatures. Application of strong magnetic fields does not
influence this anomaly. The minimum of the resistivity in ZrAs1.4Se0.5
apparently originates from interaction between the conduction electrons and
structural two-level systems. Significant disorder in the As-Se substructure is
inferred from X-ray diffraction and electron microprobe studies
Nucleation of a sodium droplet on C60
We investigate theoretically the progressive coating of C60 by several sodium
atoms. Density functional calculations using a nonlocal functional are
performed for NaC60 and Na2C60 in various configurations. These data are used
to construct an empirical atomistic model in order to treat larger sizes in a
statistical and dynamical context. Fluctuating charges are incorporated to
account for charge transfer between sodium and carbon atoms. By performing
systematic global optimization in the size range 1<=n<=30, we find that Na_nC60
is homogeneously coated at small sizes, and that a growing droplet is formed
above n=>8. The separate effects of single ionization and thermalization are
also considered, as well as the changes due to a strong external electric
field. The present results are discussed in the light of various experimental
data.Comment: 17 pages, 10 figure
Rough Fibrils Provide a Toughening Mechanism in Biological Fibers
Spider silk is a fascinating
natural composite material. Its combination
of strength and toughness is unrivalled in
nature, and as a result, it has gained considerable
interest from the medical, physics,
and materials communities. Most of this
attention has focused on the one to tens of
nanometer scale: predominantly the primary
(peptide sequences) and secondary (ÎČ sheets,
helices, and amorphous domains) structure, with some insights into tertiary structure (the
arrangement of these secondary structures) to describe the origins of the mechanical and
biological performance. Starting with spider silk, and relating our findings to collagen fibrils,
we describe toughening mechanisms at the hundreds of nanometer scale, namely, the fibril
morphology and its consequences for mechanical behavior and the dissipation of energy.
Under normal conditions, this morphology creates a nonslip fibril kinematics, restricting
shearing between fibrils, yet allowing controlled local slipping under high shear stress,
dissipating energy without bulk fracturing. This mechanism provides a relatively simple target
for biomimicry and, thus, can potentially be used to increase fracture resistance in synthetic
materials
Fabrication of composites via spouted bed granulation process and simulation of their micromechanical properties
Mineralized structures in nature: Examples and inspirations for the design of new composite materials and biomaterials
The Conservation Status of Marine Bony Shorefishes of the Greater Caribbean
The greater Caribbean biogeographic region covered in this report (representing 38 countries and territories) encompasses an outstanding marine bony shorefish richness of approximately 1,360 species, with many (53%) being endemic. This report provides an overview of the conservation status of greater Caribbean shorefishes, with detailed information available through the IUCN Red List, and gives recommendations
Polymorphism of CaCO3 and microstructure of the shell of a Brazilian invasive mollusc (Limnoperna fortunei)
The in-plane elastic properties of hierarchical composite cellular materials: Synergy of hierarchy, material heterogeneity and cell topologies at different levels
FO and EB are supported by the Queen Mary University of London Start-Up grant for new academics.
NMP is supported by the European Research Council (ERC StG Ideas 2011 BIHSNAM n. 279985, ERC PoC 2015 SILKENE nr. 693670), by the European Commission under the Graphene Flagship (WP14 Polymer Nanocomposites, n. 696656)
Advances in modelling of biomimetic fluid flow at different scales
The biomimetic flow at different scales has been discussed at length. The need of looking into the biological surfaces and morphologies and both geometrical and physical similarities to imitate the technological products and processes has been emphasized. The complex fluid flow and heat transfer problems, the fluid-interface and the physics involved at multiscale and macro-, meso-, micro- and nano-scales have been discussed. The flow and heat transfer simulation is done by various CFD solvers including Navier-Stokes and energy equations, lattice Boltzmann method and molecular dynamics method. Combined continuum-molecular dynamics method is also reviewed
Bio-inspired nacre-like composites via simple, fast, and versatile techniques such as doctor-blading
Theoretical and experimental studies show that the high performance of biological composites such as nacre and bone originates from a sophisticated microstructure, where hard and stiff inclusions form a staggered, brick wall-like structure within a softer and more deformable matrix. This morphology results in outstanding combinations of stiffness, strength and toughness, and therefore it is very attractive to duplicate it in engineering composites. Here, we demonstrate how simple, fast and versatile techniques such as doctor-blading can be used to make such bio-inspired composites. We fabricated and characterized composites made of micron-sized alumina tablets embedded in epoxy matrices. Scanning Electron Microscopy (SEM) images show that the tablets are well dispersed, aligned, and staggered through the polymer matrix resulting in a nacre-like material. The tensile behavior of these composites shows a good combination of stiffness, strength and energy dissipation. We also developed finite element models of the staggered microstructure, which properly capture the interactions between inclusions and the effects of mineral concentration. These models can be used to optimize the microstructure and fully harness the nacre-like structure and mechanisms, in new materials with applications in aerospace, defense or biomedical engineering.</p
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